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What is a kidney stone?

A kidney stone is a solid piece of material that forms in a kidney when substances that are normally found in the urine become highly concentrated. A stone may stay in the kidney or travel down the urinary tract. Kidney stones vary in size. A small stone may pass out of the body causing little or no pain. A larger stone may get stuck along the urinary tract and can block the flow of urine, causing severe pain or blood that can be seen in the urine.

What is the urinary tract?

The urinary tract is the body’s drainage system for removing wastes and extra water. The urinary tract includes two kidneys, two ureters, a bladder, and a urethra. The kidneys are a pair of bean-shaped organs, each about the size of a fist and located below the ribs, one on each side of the spine, toward the middle of the back. Every minute, a person’s kidneys filter about 3 ounces of blood, removing wastes and extra water. The wastes and extra water make up the 1 to 2 quarts of urine an adult produces each day. Children produce less urine each day; the amount produced depends on their age. The urine travels from the kidneys down two narrow tubes called the ureters. The urine is then stored in a balloonlike organ called the bladder. When the bladder empties, urine flows out of the body through a tube called the urethra at the bottom of the bladder.The kidneys remove wastes and extra
water from the blood to form urine. Urine
travels from the kidneys to the bladder
through the ureters.

Are kidney stones common in children?

No exact information about the incidence of kidney stones in children is available, but many kidney specialists report seeing more children with this condition in recent years. While kidney stones are more common in adults, they do occur in infants, children, and teenagers from all races and ethnicities

What causes kidney stones in children?

Kidney stones can form when substances
in the urine—such as calcium, magnesium,
oxalate, and phosphorous—become highly
concentrated due to one or more causes:

Defects in the urinary tract may block
the flow of urine and create pools of
urine. In stagnant urine, stone-forming
substances tend to settle together into
stones. Up to one-third of children who
have stones have an anatomic abnormality
in their urinary tract.

Kidney stones may have a genetic cause.
In other words, the tendency to form
stones can run in families due to inherited
factors.

An unhealthy lifestyle may make children
more likely to have kidney stones.
For example, drinking too little water or
drinking the wrong types of fluids, such
as soft drinks or drinks with caffeine,
may cause substances in the urine to
become too concentrated. Similarly,
too much sodium, or salt, in the diet
may contribute to more chemicals in the
urine, causing an increase in stone formation.
Some doctors believe increases
in obesity rates, less active lifestyles, and
diets higher in salt may be causing more
children to have kidney stones.

Sometimes, a urinary tract infection
can cause kidney stones to form.
Some types of bacteria in the urinary
tract break down urea—a waste product
removed from the blood by the
kidneys—into substances that form
stones.

Some children have metabolic disorders
that lead to kidney stones. Metabolism
is the way the body uses digested
food for energy, including the process
of breaking down food, using food’s
nutrients in the body, and removing the
wastes that remain. The most common
metabolic disorder that causes kidney
stones in children is hypercalciuria,
which causes extra calcium to collect in
the urine. Other more rare metabolic
conditions involve problems breaking
down oxalate, a substance made in the
body and found in some foods. These
conditions include hyperoxaluria, too
much oxalate in the urine, and oxalosis,
characterized by deposits of oxalate and
calcium in the body’s tissues. Another
rare metabolic condition called cystinuria
can cause kidney stones. Cystinuria
is an excess of the amino acid cystine in
the urine. Amino acids are the building
blocks of proteins.

What are the signs and symptoms of kidney stones in children?

Children with kidney stones may have pain
while urinating, see blood in the urine, or
feel a sharp pain in the back or lower abdomen.
The pain may last for a short or long
time. Children may experience nausea and
vomiting with the pain. However, children
who have small stones that pass easily
through the urinary tract may not have
symptoms at all.

What types of kidney stones occur in children?

Four major types of kidney stones occur in
children:

Calcium stones are the most common
type of kidney stone and occur in two
major forms: calcium oxalate and
calcium phosphate. Calcium oxalate
stones are more common. Calcium oxalate
stone formation has various causes,
which may include high calcium excretion,
high oxalate excretion, or acidic
urine. Calcium phosphate stones are
caused by alkaline urine.

Uric acid stones form when the urine
is persistently acidic. A diet rich in
purines—substances found in animal
proteins such as meats, fish, and
shellfish—may cause uric acid. If uric
acid becomes concentrated in the urine,
it can settle and form a stone by itself or
along with calcium.

Struvite stones result from kidney infections.
Eliminating infected stones from
the urinary tract and staying infectionfree
can prevent more struvite stones.

Cystine stones result from a genetic
disorder that causes cystine to leak
through the kidneys and into the urine
in high concentration, forming crystals
that tend to accumulate into stones.

How are kidney stones in children diagnosed?

The process of diagnosing any illness begins
with consideration of the symptoms. Pain
or bloody urine may be the first symptom.
Urine, blood, and imaging tests will help
determine whether symptoms are caused by
a stone. Urine tests can be used to check
for infection and for substances that form
stones. Blood tests can be used to check for
biochemical problems that can lead to kidney
stones. Various imaging techniques can be
used to locate the stone:

Ultrasound uses a device, called a
transducer, that bounces safe, painless
sound waves off organs to create an
image of their structure. An abdominal
ultrasound can create images of
the entire urinary tract. The procedure
is performed in a health care
provider’s office, outpatient center, or
hospital by a specially trained technician,
and the images are interpreted
by a radiologist—a doctor who specializes
in medical imaging; anesthesia is
not needed. The images can show the
location of any stones. This test does
not expose children to radiation, unlike
some other imaging tests. Although
other tests are more useful in detecting
very small stones or stones in the lower
portion of the ureter, ultrasound is
considered by many health care providers
to be the best screening test to look
for stones.

Computerized tomography (CT)
scans use a combination of x rays and
computer technology to create threedimensional
(3-D) images. A CT scan
may include the injection of a special
dye, called contrast medium. CT scans
require the child to lie on a table that
slides into a tunnel-shaped device where
the x rays are taken. The procedure is
performed in an outpatient center or
hospital by an x-ray technician, and the
images are interpreted by a radiologist;
anesthesia is not needed. CT scans may
be required to get an accurate stone
count when children are being considered
for urologic surgery. Because CT
scans expose children to a moderate
amount of radiation, health care providers
try to reduce radiation exposure in children by avoiding repeated CT scans,
restricting the area scanned as much
as possible, and using the lowest radiation
dose that will provide the needed
diagnostic information.

X-ray machines use radiation to create
images of the child’s urinary tract. The
images can be taken at an outpatient
center or hospital by an x-ray technician,
and the images are interpreted by
a radiologist; anesthesia is not needed.
The x rays are used to locate many kinds
of stones. A conventional x ray is generally
less informative than an ultrasound
or CT scan, but it is less expensive and
can be done more quickly than other
imaging procedures.

How are kidney stones in children treated?

The treatment for a kidney stone usually
depends on its size and what it is made of,
as well as whether it is causing symptoms of
pain or obstructing the urinary tract. Small
stones usually pass through the urinary tract
without treatment. Still, children will often
require pain control and encouragement to
drink lots of fluids to help move the stone
along. Pain control may consist of oral or
intravenous (IV) medication, depending
on the duration and severity of the pain.
IV fluids may be needed if the child becomes
dehydrated from vomiting or an inability to
drink. A child with a larger stone, or one
that blocks urine flow and causes great pain,
may need to be hospitalized for more urgent
treatment. Hospital treatments may include
the following:

Shock wave lithotripsy (SWL). A
machine called a lithotripter is used by
the doctor to crush the kidney stone. In
SWL, the child lies on a table or, less
commonly, in a tub of water above the
lithotripter. The lithotripter generates
shock waves that pass through the
child’s body to break the kidney stone
into smaller particles to pass more readily
through the urinary tract. Children
younger than age 12 may receive general
anesthesia during the procedure.
Older children usually receive an IV
sedative and pain medication.

Removal of the stone with a ureteroscope.
A ureteroscope is a long, tubelike
instrument used to visualize the
urinary tract. After the child receives a
sedative, the doctor inserts the ureteroscope
into the child’s urethra and slides
the scope through the bladder and into
the ureter. Through the ureteroscope,
which has a small basket attached to the
end, the doctor may be able to see and
remove the stone in the ureter.Ureteroscopic stone removal

Lithotripsy with a ureteroscope.
Another way to treat a kidney stone
through a ureteroscope is to extend a
flexible fiber through the scope up to
the stone. The fiber is attached to a
laser generator. Instead of shock waves,
the fiber delivers a laser beam to break
the stone into smaller pieces that can
pass out of the body in the urine. The
child may receive general anesthesia or
IV sedation.Percutaneous nephrolithotomy

Percutaneous nephrolithotomy. In this
procedure, a tube is inserted directly
into the kidney through an incision in
the child’s back. Using a wire-thin viewing
instrument called a nephroscope,
the doctor locates and removes the
stone. For large stones, an ultrasonic
probe that acts as a lithotripter may
be needed to deliver shock waves that
break the stone into small pieces that
can be removed more easily. Children
receive general anesthesia for percutaneous
nephrolithotomy. Often, children
stay in the hospital for several days after
the procedure and may have a small
tube called a nephrostomy tube inserted
through the skin into the kidney. The
nephrostomy tube drains urine and
any residual stone fragments from the
kidney into a urine collection bag. The
tube usually is left in the kidney for
2 or 3 days while the child remains in
the hospital.Nephrostomy tube

How are kidney stones in children prevented?

To prevent kidney stones, health care providers
and their patients must understand what
is causing the stones to form. Especially in
children with suspected metabolic abnormalities
or with recurrent stones, a 24-hour
urine collection is obtained to measure daily
urine volume and to determine if any underlying
mineral abnormality is making a child
more likely to form stones. Based on the
analysis of the collected urine, the treatment
can be individualized to address a metabolic
problem.

In all circumstances, children should drink
plenty of fluids to keep the urine diluted and
flush away substances that could form kidney
stones. Urine should be almost clear.

Eating, Diet, and Nutrition

Families may benefit from meeting with a
dietitian to learn how dietary management
can help in preventing stones. Depending on
the underlying cause of the stone formation,
medications may be necessary to prevent
recurrent stones. Dietary changes and medications
may be required for a long term or,
quite often, for life. Some common changes
include the following:

Children who tend to make calcium
oxalate stones or have hypercalciuria
should eat a regular amount of dietary
calcium and limit salt intake. A thiazide
diuretic medication may be given to
some children to reduce the amount of
calcium leaking into the urine.

Children who have large amounts of
oxalate in the urine may need to limit
foods high in oxalate, such as chocolate,
peanut butter, and dark-colored soft
drinks.

Children who form uric acid or cystine
stones may need extra potassium citrate
or potassium carbonate in the form of
a pill or liquid medication. Avoiding
foods high in purines—such as meat,
fish, and shellfish—may also help prevent
uric acid stones.

Hope through Research

The National Institute of Diabetes and
Digestive and Kidney Diseases (NIDDK),
one of the National Institutes of Health, supports
research aimed at better understanding
and preventing kidney stones in children.
Researchers supported by the NIDDK have
identified three proteins that inhibit the
formation of calcium oxalate stones. Conventional
urine tests do not provide information
about the presence or absence of
these proteins. Developing a test for these
proteins that can be used in the clinical setting
will help health care providers identify
children at risk for stone formation so they
can manage that risk.

Participants in clinical trials can play a more
active role in their own health care, gain
access to new research treatments before
they are widely available, and help others
by contributing to medical research. For
information about current studies, visit
www.ClinicalTrials.gov.

You may also find additional information about this
topic by visiting MedlinePlus www.medlineplus.gov.

This publication may contain information about
medications. When prepared, this publication
included the most current information available.
For updates or for questions about any medications,
contact the U.S. Food and Drug Administration tollfree
at 1–888–INFO–FDA (1–888–463–6332) or visit www.fda.gov. Consult your health care provider for more information.

National Kidney and Urologic Diseases Information Clearinghouse

The National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC) is a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The NIDDK is part of the National Institutes of Health of the U.S. Department of Health and Human Services. Established in 1987, the Clearinghouse provides information about diseases of the kidneys and urologic system to people with kidney and urologic disorders and to their families, health care professionals, and the public. The NKUDIC answers inquiries, develops and distributes publications, and works closely with professional and patient organizations and Government agencies to coordinate resources about kidney and urologic diseases.

This publication is not copyrighted. The Clearinghouse encourages users of this publication to duplicate and distribute as many copies as desired.